The invention relates to the inspection of the rails of railroad tracks, and more particularly to a process for the automatic recognition of discontinuities or irregularities and especially the fished joints of the rails of railroad tracks, as well as to a device for the implementation of such a process.
The stresses and dynamic overloads to which the track is subjected cause the development of internal faults in the rail, such as oval flaws, horizontal, transverse or longitudinal cracks, star-shaped cracks, etc.
It is important to be able to detect these faults on the track using a non-destructive method, in order to be able to change defective sections of rail in time while distinguishing as far as possible between faults and joints or other discontinuities that can occur in the rails.
The most widely used method of non-destructive testing of the internal state of rails on the track is the sounding of the rail by ultrasonics. This technique consists in placing in contact with the rail head transmitting, receiving or transmitting-receiving probes, the orientation of which is adapted to the type of fault being looked for.
In general, light instruments employed by an operator or heavy instruments carried in rail cars are used.
In the first case, the operator sounds one or two lines of rail simultaneously using ultrasonic instruments adapted to this technique. A probe is placed in contact with the running surface of each rail. The operator advances slowly, at a speed of about 3 km/h, and checks all the ultrasonic detections on the screen of the instrument. He therefore has to analyse the results displayed by the instrument and correlate them with the rail. In fact not every ultrasonic detection is necessarily associated with an internal fault. For example the fishing holes in the rails appear very clearly on the instrument but must not be considered as faults. Another example is that relating to the detection of the ends of rails when these are fished. The rail, in this case, behaves like a rail with a vertical break through its full height. In this case the ultrasonic instrument indicates sounding anomalies. The operator can easily see the difference between a broken rail and the end of a rail when it is fished. He interprets the results of the ultrasonic sounding in order to sort certain data, helped by the fact that he can see the rail.
On the other hand, in the second case, when the detection equipment is carried in a sounding rail car, this analysis is made very difficult because of the speed at which the machine moves (which can be of the order of 30 to 50 km/h). It became necessary in this case to develop a process which enables the real faults in the rail to be distinguished from all the detections made by the instruments in order to sort the results automatically.